Dextranases synthesized by many different dental plaque bacteria appear to function in the formation of fermentable carbohydrates from alpha 1,6 glucans. S. mutans dextranase has also been implicated in the formation of glucosyltransferase-mediated insoluble glucans which appear to be necessary for optimal colonization of tooth surfaces by S. mutans. The purpose of the present investigation is to determine the importance of dextranases in dental plaque and in a vaccine to protect against S. mutans infection. Initial studies involve the purification and characterization of dextranase from a high producing mutant of S. mutans strain 6715, and the comparison of the S. mutans enzyme with dextranases present in monkey dental plaque formed under various dietary conditions. The effect of purified S. mutans dextranase on glucan formation and sucrose-mediated adherence by mutants of strain 6715, defective in the synthesis of dextranase will also be determined.